Iron Fischer-Tropsch (F-T) catalysts have generally been preferred commercially over cobalt based catalysts and are presently the only commercial F-T catalyst used.
While cobalt catalysts have the benefit of higher activity and better selectivity to motor fuels they suffer from their inherent production of excess methane (an undesirable product) as well as the paraffinic nature of the product. It would be an important catalyst improvement if a stable cobalt F-T catalyst was discovered which demonstrated reduced methane production, increased C5+ yield and improved olefin content, especially in the C5- range.
Prior art teaching for the use of promoted cobalt oxide in the Fischer Tropsch process has been well established, including the commercial use of a thorium, magnesium promoted cobalt kieselguhr catalyst in Germany in the 1930's and 40's. A large number of literature studies have been published and patents issued in the area, many dealing with the use of various promoters to improve catalyst performance.
An excellent review of past publications on cobalt Fischer-Tropsch catalyst was reported by R. B. Anderson, "The Fischer-Tropsch Synthesis", Academic Press, Orlando FL, 1984. In the review are lists of promoters and catalysts studied in the past, included are sightings of the use of Mn and Zr promoters. Listed below is a summary of the information presented in this article related to the use of the Mn and Zr promoters. Fischer and Koch showed Mn added to a cobalt kieselguhr catalyst was effective at shifting the product distribution toward heavier product as was also observed for the catalysts in this invention. Work by Eidus and Bulanova showed a similar effect on the addition of ZrO2 to the same type of catalyst, this was not observed upon our addition of ZrO2 to the Mn promoted Co/TC-123 catalyst system. No work to our knowledge has been reported on the use of a combined Mn and Zr promoted catalyst
Dent, A. L. and Lin, M., Adv. Chem. Ser. 178,47 (1979) reported that the addition of Mn to a cobalt alumina catalyst increased the olefin content in the product, which is consistent with our data.
The only prior art of which the applicants are aware relating Zr for improving the stability of a cobalt F-T catalyst was reported by Eidus and Bulanova U.S.S.R. 150,102, Sept. 26, 1962, Appl. Nov. 27, 1954. In this work Zr was used in place of thorium to reduce the sensitivity of the catalyst to super heating. The applicants are not aware of any prior art which teaches the use of Mn to improve cobalt catalyst stability.